A sucker rod is a rigid rod used in the oil industry to join together the surface and downhole components of a reciprocating piston pump installed in an oil well. These rods are typically between 25 and 30 feet (7 to 9 meters) in length, and threaded at both ends.
Certain methods of remanufacturing sucker rods for re-use comprise eliminating or reducing the fatigue stress in the used rods by a method involving thermally treating the rods at a temperature between about 200° C. and about 650° C. for 15 to 30 minutes. Typically this consists of normalization, upgrading or tempering, with reference to the material or rods remanufactured. After thermal treatment the rods are straightened while still hot to achieve the required straightness. Additionally, straightening while still hot allows for the removal of stress which can occur otherwise during the course of the straightening procedure.
Other methods used in the remanufacturing of rods such as sucker rods comprise the use of a device with two heads that have the ability to clamp two ends of the rod in need of treatment or modification. In this methodology, typically one head turns uncontrollably with the rod treated along its longitudinal central line. However, use of the aforementioned device can result in deformation of standard length sucker rods due to tension and torsion, even though cold working the rod's surface would improve the fatigue strength and the efficiency.
Typically the main process of reclaiming or reconditioning a used rod utilized in oil pump wells comprises obtaining the rod, cleaning the rod to remove contaminates from use in oil extraction, performing an inspection of the rod to determine if the rod should be reconditioned or discarded, categorizing the rod into steel class, heating the rod until plastic deformation, shaping the rod, cooling the rod and cutting the rod into the desired length. Embodiments of the invention pertain to a method for reconditioning a used sucker rod having a given diameter.
Typically, on pre-cleaned rods are found contaminates such as paraffin. Further, the cleaning process wherein contaminates are removed often comprises washing the rod with an organic compound. One organic compound typically used is kerosene. Other chemicals known in the art that are useful for cleaning rods are chemicals such as naptha and caustic acid. However, all of these aforementioned methods of cleaning leave toxic or caustic residue as a byproduct of the cleaning process.
Additionally, such cleaning agents can render chemicals attached to the rods soluble in organic compounds or in caustic acids. Such chemicals are often themselves toxic to the environment or pose cleanup problems at the cleaning facility.
It would therefore be advantageous to reduce the contamination to the environment and to the cleaning facility by the utilization of non-toxic cleaners and cleaners which do not result in solubility of contaminates from rods such as sucker rods. One such cleaning material is the use of non-toxic inorganic cryogenic liquids.
Because there is no secondary waste stream, non-toxic inorganic cryogenic liquids are advantageous from a cleaning standpoint. Typically, the only waste to clean up afterward is the grime, paraffin, rust or whatever contaminant was removed. Likewise, in the restoration applications total job time is greatly reduced due to the fact there is very little post-blast cleanup required.
Cryogenic liquid applications to the surface of sucker rods can produce an expansion factor upon making contact with the rods themselves. This is because the cryogenic liquids can change and expand from a liquid to a gas. Depending on the type of cryogenic liquid being used, and the air pressure and nozzle selected, the liquid can travel at speeds between 600 and 800 feet per second. Assuming the liquid is able to initially penetrate the contaminant, this expansion occurs at the underlying substrate, thus lifting the contaminant off. Alternatively or additively, the cryogenic liquid can produce a thermal shock effect, as the particles are at sub-zero temperatures.
Cryogenic liquids impacting a sucker rod or other pump rod surface with contaminants typically removes contaminates in one of three ways: via kinetic energy, via thermal shock or via a thermal-kinetic effect. Kinetic energy transfers the energy of the accelerated cryogenic liquid as it hits the surface of the rod to be cleaned during the blasting process; this is akin to a pressure washing effect. However, in some applications, a high pressure cryogenic liquid is not used. Likewise, thermal shock occurs when certain cryogenic liquids strike a much warmer contaminated surface during the blasting process. The cold temperature of the cryogenic liquid causes the bond between the surface being cleaned and the contaminants to weaken. This effect aids in the release of the contaminant when struck by the liquid during the blasting process. The thermal-kinetic effect combines the impact of evaporation and the rapid heat transfer discussed above. When the pressurized cryogenic liquid hits the contaminated surface, the vapor expands fast enough that micro-explosions occur which take off the contaminants from the rod.
In the embodiments herein discussed, the non-toxic inorganic cryogenic liquids are gasses which liquefy below the freezing point of water. Preferable examples of non-toxic liquids with an evaporation point below the freezing point of water which can be utilized in the present invention include: liquid nitrogen, liquid oxygen, liquid hydrogen, liquid helium, liquid neon, liquid argon, liquid krypton, liquid xenon, and the like.